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CD14 , TLR4 and TRAM Show Different Trafficking Dynamics During LPS Stimulation
Author(s) -
Klein Dionne C.G.,
Skjesol Astrid,
KersRebel Esther D.,
Sherstova Tatyana,
Sporsheim Bjørnar,
Egeberg Kjartan W.,
Stokke Bjørn T.,
Espevik Terje,
Husebye Harald
Publication year - 2015
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/tra.12274
Subject(s) - endosome , trif , microbiology and biotechnology , tlr4 , endocytic cycle , biology , signal transducing adaptor protein , endocytosis , toll like receptor , clathrin , signal transduction , receptor , innate immune system , intracellular , biochemistry
Toll‐like receptor 4 ( TLR4 ) is responsible for the immediate response to Gram‐negative bacteria and signals via two main pathways by recruitment of distinct pairs of adaptor proteins. Mal‐ MyD88 [Mal (MyD88‐adaptor‐like) ‐ MYD88 (Myeloid differentiation primary response gene (88))] is recruited to the plasma membrane to initiate the signaling cascade leading to production of pro‐inflammatory cytokines while TRAM‐TRIF [TRAM (TRIF‐related adaptor molecule)‐TRIF (TIR‐domain‐containing adapter‐inducing interferon‐β)] is recruited to early endosomes to initiate the subsequent production of type I interferons. We have investigated the dynamics of TLR4 and TRAM during lipopolysaccharide ( LPS ) stimulation. We found that LPS induced a CD14 ‐dependent immobile fraction of TLR4 in the plasma membrane. Total internal reflection fluorescence microscopy ( TIRF ) revealed that LPS stimulation induced clustering of TLR4 into small punctate structures in the plasma membrane containing CD14 / LPS and clathrin, both in HEK293 cells and the macrophage model cell line U373‐CD14 . These results suggest that laterally immobilized TLR4 receptor complexes are being formed and prepared for endocytosis. RAB11A was found to be involved in localizing TRAM to the endocytic recycling compartment ( ERC ) and to early sorting endosomes. Moreover, CD14 / LPS but not TRAM was immobilized on RAB11A ‐positive endosomes, which indicates that TRAM and CD14 / LPS can independently be recruited to endosomes.